Autoconfiguration of control connections in an exchange

ABSTRACT

The invention concerns autoconfiguration of control connections in a telecommunication switch. Multiplexers ( 31, 32, 33 ) themselves and without external control information find out which ports of the switching fabric ( 34 ) they are in connection with. After finding out the ports, logical connections are established. Each multiplexer forms probe cells addressed to each of the ports ( 0, 1, 2 ). Each probe cell includes one port index, preferably in the header. The switching fabric ( 34 ) switches the probe cell to that output port which has been indicated in the header of the probe cell. Thus, those probe cells fed from a port into the switching fabric are returned to the same port if the target in the header is the same as the port number. In consequence of this, the multiplexer receives only the same kind of probe cells. After the connection ports have been determined, a logical connection between each of the multiplexers ( 31, 32, 33 ) and the operation and maintenance unit ( 35 ) is established. The processor units connected to the multiplexers can now receive configuration information and instructions from the operation and maintenance unit ( 35 ).

FIELD OF THE INVENTION

The present invention relates to establishing virtual connectionsbetween a plurality of telecommunication equipment. In particular, theinvention relates to internal traffic in a node of a broadbandtelecommunication network, such as an ATM node.

BACKGROUND OF THE INVENTION

The basic function of a modern digital exchange is to connect theexchange input port to the correct output port, in other words, toconnect an incoming call on a specific incoming circuit to an outgoingcall on a specific outgoing circuit. The core of the system is theexchange control, whose functions have been distributed over a pluralityof units, each carrying out its own task. As examples of such units area unit controlling the switching matrix, signaling units carrying outdifferent types of signaling and supervision at the input and outputsides, a unit collecting call-specific charging data, a unit gatheringstatistics, etc. Each unit comprises at least one central processingunit CPU, a bus, and memory. Thus, each unit actually constitutes acomputer.

In addition, the exchange comprises an Operation and Maintenance Unit(O&M), which takes care of the maintenance of the system.

Apart from the type described above, the telecommunication network nodesmay also be ATM nodes (Asynchronous Transfer Mode). ATM is aconnection-oriented, packet switched, general purpose, and scalable datatransmission method in which information is sent in fixed-length cells.The cell consists of a five-byte-long header and a 48-byte-longinformation section. The header fields include a Virtual Path Indicator(VPI) and a Virtual Channel Indicator (VCI). At the ATM switch, thecells are transferred from a logical input channel to one or morelogical output channels. The logical channel consists of the number ofthe physical link (e.g. optical cable) and the channel identifier onthis link, in other words the VPI/VCI information. One physical transfermedium, such as an optical cable, may comprise a plurality of virtualpaths VP, and each virtual path comprises a plurality of virtualchannels VC.

Because the cells are of a fixed length, the connections at ATM switchescan be performed at hardware level on the basis of the cell header, andtherefore at very high speed. Cells belonging to different connectionsare distinguished from one another on the basis of the virtual path(VPI) and the virtual channel (VCI) identifier. As the connection is setup, a fixed route is determined through the network, i.e. a virtual linkalong which the cells of the connection are routed. Based on the VPI/VCIvalues, the cells are switched at the network nodes. The VPI/VCI valuesare transmission link specific and consequently usually change inconnection with switching at the VP or VC level. At the end of the datatransfer, the connection is released.

FIG. 1 illustrates a simplified ATM switch. It consists of input stagesand output stages, into which the physical input and output lines areconnected, and of a switching fabric. The physical line can consist ofany suitable medium, of an optical fiber as shown in the figure, of atwisted pair, of a coaxial cable, for example. As an example the mediumherein is the optical fiber. The input and output stages constitute theexternal network interfaces. The interface type may be either UNI (UserNetwork Interface) or NNI (Network Node Interface). The input stagereads the address information, i.e. the VPI and VCI identifiers, of thecell received from the input link and converts them into new VPI/VCIvalues which the output stage inserts into the header of the cell sentto the output link.

The software of the switch is distributed over functional blocks,processor units 1, . . . N., handled by computers. The computers arenearly always of the embedded type, meaning that display units and otherperipheral devices are not required.

FIG. 2 is a more detailed illustration of an ATM switch. A cell, eitherof the UNI or NNI type, from optical fibre 20 is received at circuit 21of the PHY layer (Physical Layer) that terminates the line. The PHYcarries out transmission system specific tasks at the bit level and isresponsible for cell adaptation to each of the transmission systems, aswell as for cell masking, cell header error checks, and cell ratejustification.

From circuit 21 of the PHY layer, the cell passes to circuit 22 of theATM layer. The ATM layer only deals with the cell header, its tasksbeing cell switching, multiplexing and demultiplexing, and cell headergeneration and removal. Above the ATM layer, the AAL (ATM AdaptationLayer) fragments the higher layer frames and reassembles them at theother end, in other words, carries out the SAR (Segmentation andRe-assembly) function.

Circuit 22 of the ATM layer sends the cell to the input buffer of ATMswitching fabric 23. From there, the fabric connects it to the otherside of the fabric, to output port 25. At the output port, the VPI/VCIvalue in the cell address field is examined, and the cell is transmittedto the correct virtual channel.

The processor units in FIG. 1 must be able to negotiate with each other.The most common way is to set up a dedicated common message bus, intowhich the units are connected via a bus adapter.

FIG. 3 depicts another of arranging the routing of the internal-trafficof cells through the ATM switching fabric. A group of processor units,here Processor Unit 1, . . . , Processor Unit N, are connected tomultiplexer 31, whereas a second group of units, Processor Unit A1, . .. , Processor Unit An, are connected to multiplexer 32. A third group ofunits, Processor Unit B1, . . . , Processor Unit Bn, are connected tomultiplexer 33. A multiplexer multiplexes ATM cells received from anattached group of units to an input port of ATM switching fabric 34,which routes the cells through the fabric to destination output ports.

For example, let us consider a case when processor unit 1 is sendingcells to processor unit B1 and processor unit N is sending cells toprocessor unit 2. Multiplexer 31 provides the cells with the properVPI/VCI addresses and multiplexes the cells to input port 0 of theswitching fabric. The switching fabric returns the cells addressed toprocessor unit N to output port 0. Demultiplexer 31 routes the cellsfurther to processor unit N.

Switching matrix 34 routes the cells addressed to processor unit B1 tooutput port 1, whereupon multiplexer 33, which is connected to thatport, routes the cells to target processor unit B1.

Still referring to FIG. 3, it is advantageous to form a group ofprocessor units from the units having similar processor types. Hence,processors of units from 1 to N could be general purposemicroprocessors, whereas processors of units from B1 to Bn could besignal processors.

Operation and maintenance unit 35 is also connected through multiplexer31 to port 0 of ATM switching fabric 34. The task of the operation andmaintenance unit is to ensure that the functional units of the exchangeare operating properly. In addition, the unit acts as an input andoutput device through which the operator can update software and inputinstructions to the software. For those purposes there arebi-directional control connections between the operation and maintenanceunit 35 and the processor units.

The operation and maintenance unit plays an especially important rolewhen commissioning the exchange. After the power to various units of theexchange has been switched on, the operation and maintenance unitensures that the exchange starts to operate properly.

A problem in the prior art exchanges switching packets of a fixed lengthis how to form control connections between the operation and maintenanceunit and the processor units from the time the power is switched on.These connections are needed for downloading the program code from theoperation and maintenance unit to the processor units.

FIG. 4 illustrates this problem. In reality, the problem is reduced tothat of how to establish a connection between each of the multiplexersand the operation and maintenance unit. A software application runs ineach of the multplexor units 1-N of the exchange. Accordingly, aplurality of software applications runs in operation and maintenanceunit 41. In order for the operation and maintenance unit to be able tocontrol the setting-up of the processor units, a logical channel forcommunication through the switching fabric is needed between operationand maintenance unit 41 and each of the multiplexers. After the logicalchannels have been created, the applications in processor units (seeFIG. 3) can communicate with the applications in the operation andmaintenance unit for further configuration instructions during thesetting-up process. The applications running in the processor units aredirectly connected to the operation and maintenance unit via the AAL/ATMand PHY layers.

Unfortunately, the multiplexer units can not begin creating logicalchannels because they do not know to which port of the switching fabricthey are physically connected. Due to the lack of logical channels,processor units can not receive a program code from the operation andmaintenance unit.

A prior art solution for the problem is that after switching the poweron, the operator enters information about the connection port manuallyinto each of the multiplexer units. In addition, software programsincluding configuration information are loaded manually into thememories of the processor units. Alternatively, all the program codewhich is necessary for powering up the processor units may be stored inthe flash memory of the unit. However, this solution is not acceptablebecause upgrading a program code is difficult. Hence, only a minimumamount of the program code is stored in the flash memory, the rest ofthe code is retrieved from the operation and maintenance unit.

A drawback of the known method is that entering information aboutconnection ports manually to several multiplexer units and loading theprogram code into the units are a time consuming and error-proneoperation.

SUMMARY OF THE INVENTION

The objective of the present invention is to devise a method which makespossible autoconfiguration of control connections, i.e. multiplexersthemselves and without external control information determine to whichports of the switching fabric they are connected. After the ports areknown, logical connections are established.

According to the invention, each multiplexer forms special cells whichare hereafter called probe cells. A port number is included in that partof the cell which tells the target of the probe cell. A predeterminedtermination point index in the multiplexer is also included to the probecell. Hence, the number of different probe cells is the number of theports of the switching fabric.

The invention is based on the fact that the switching fabric switchesthe probe cell to that output port the port number of which has beenindicated in the probe cell. Thus, the probe cells fed from a certainport into the switching fabric are returned to that certain port if theport number included in the probe cell is the same as the number of thatcertain port. In consequence of this, the multiplexer receives only thesame kind of probe cells and, moreover, the payload of the receivedcells tells the multiplexer to which port of the switching fabric themultiplexer has been connected. Each probe cell received from theswitching fabric includes the same termination point index. Based onthat index the multiplexer routes the received probe cells to the sameplace, preferably to the processor.

Other cells are routed to the ports the port numbers of which areincluded to the probe cells. As a result, a multiplexer receives fromthe switching fabric not only probe cells which it has itself sent tothe switching fabric but also cells which have been sent to theswitching fabric by other multiplexers connected to other ports.However, all the received cells are addressed to the same port, whichcorroborates that the multiplexer has been connected to the portindicated in the received cells.

After the connection ports have been determined, a logical connectionbetween each of the multiplexers and the operation and maintenance unitis established. The processor units connected to the multiplexers cannow receive configuration information and instructions from theoperation and maintenance unit.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in closer detail with reference to theattached schematic drawings, in which

FIG. 1 illustrates an ATM switch,

FIG. 2 illustrates network connections of the ATM switch,

FIG. 3 depicts the connection of processor units in a switch,

FIG. 4 shows the connection between an operation and maintenance unitand multiplexers,

FIG. 5 show an index table in a multiplexer,

FIG. 6 depicts the starting point of the invention,

FIG. 7 illustrates the forming of a probe cell,

FIG. 8 illustrates a response to the sending of the probe cells, and

FIG. 9 shows the filling of the index tables.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described in greater detail. It is known tothose skilled in the art that a multiplexer includes a plurality ofindexed termination points.

FIG. 5 depicts the general concept of the termination points. Atermination point connects a virtual channel from the side of theswitching fabric to a channel between the multiplexer and a processorunit. One can imagine that a processor unit connected to terminationpoint 1 will send information to a multiplexer connected to port K ofthe switching fabric and further to the processor unit, which isconnected to termination point p in the multiplexer at the opposite end.That's why the information about the multiplexer at the opposite end,i.e. port index K and termination point p, is linked to terminationpoint 1. In this manner the first row of the table is created. Furtherrows can be created accordingly. In this manner each processor unit cansend information to any of the other processor units via a virtualchannel which is determined by the port and the termination point of themultiplexer at the opposite end. It is worth noting that if a processorunit communicates with another processor unit connected to the samemultiplexer, packets travel to the switching fabric, which returns themto the proper termination point.

FIG. 6 is basically the same as FIG. 3 except that the afore-describedtermination point tables are included in multiplexers 31, 32, and 33. Aprerequisite for the invention is that the port of the switching fabricis known to which the operation and maintenance unit is connected viathe multiplexer. In FIG. 6 that port is denoted with numeral 0. Hence,the system knows that operation and maintenance unit 35 is alwaysconnected to port 0. Further, internal processor 61 of multiplexer 31 isconnected to the predetermined termination point X.

The internal processors of multiplexers 32 and 33 are also connected totermination point X of said multiplexers. The first row of indexes inthe tables of the multiplexers can now be formed from termination pointX, from index 0 and from index Y+?. Index 0 refers to port 0 at theopposite end of a logical channel, i.e. to multiplexer 31, and y+?refers to termination point Y+? in this multiplexer.

The reason for indexing termination points by Y+? is that the questionmark will be replaced with an actual port number after it has beendetermined. More rows, i.e. more termination points, can then beactivated easily as will be explained later.

In order to find out the port to which a multiplexer is connected, themultiplexer adds an extra row to the table. This is illustrated in FIG.7. The row includes only one index Z, i.e. the termination point indexZ. This row is connected with line 72 to the processor 73 whichindicates that the cells arriving from the switching fabric andaddressed to the termination point Z, are transferred directly to theprocessor. This function will be explained in more detail below.

Based on the index in row 1, processor 73 of the multiplexer forms probepacket or probe cell 71. The probe cell contains the index value of aport variable and the index Z. The index Z refers to the targettermination point of the multiplexer. Preferably the index value and theindex Z are attached to the header of the cell type used in the systemas shown in the figure. The port variable can have any of the port indexvalues of the switching fabric. Hence, the number of different probepackets is the same as the number of ports in the switching fabric. Ifthe number of ports is three, the multiplexer sends a burst of threedifferent types of probe cells to the switching fabric.

FIG. 8 depicts the transmission of the probe cells. Note, that the probecells are transmitted directly without terminating to any terminationpoint. This is depicted with dotted line 810. It is still assumed thatthe exemplary switching fabric has three ports as shown in FIG. 6.Further, the multiplexer considered is multiplexer 33. Multiplexer 33sends three types of probe cells. The target port of the first type 801is port 0 and the target termination point is Z. The payload can beempty but some information can also be inserted into it, the target portnumber for example. The target port of the second type 802 is port 2 andthe target termination point is Z Accordingly, the target port of thethird type 803 is port 2 and the target termination point is Z.

Aternatively, it is possible that the processor sends the probe cells ina conventional ATM-channel which are terminated in the ATM layer. Inthat case the probe cells are formed so that the header includes thetarget termination point Z and a port variable which can have any one ofthe port indexes whereas the payload contains the target port number.

The switching fabric receives a burst of the above-mentioned probe cellsand routes them to the destination ports indicated in the headers of theprobe cells. As a result, the first types of the probe cells are routedto port 0, the second type of the probe cells are routed to port 1, andthe third type 803 of the probe cells are routed to port 2. So,multiplexer 33 receives from the switching fabric the same probe cells803 which the multiplexer transmitted to the switching fabric. In themultiplexer the received cells are terminated to that termination pointwhich is indicated in the received cells. Hence, the cells areterminated to the termination Z from which the cells are furthertransferred to the processor 63. This is depicted with line 811 in thefigure. Multiplexer 33, or in this example the processor, uncovers fromthe received probe cells information and finds out that the portvariables in the cells are the same, namely port index 2. Now themultiplexer is able to determine that it has been connected to port 2 ofthe switching fabric.

In addition, the multiplexer also receives those probe cells, denotedwith reference numeral 804, which have the destination port index 2 inthe header but which were transmitted by the other multiplexers.Uncovering the contents of those probe cells also results in port index2. Hence, that result further confirms that the multiplexer has beenconnected to port 2.

In the above-described manner each of multiplexers finds out the port towhich the multiplexer is connected.

There may also be one or more multiplexers which are not connected tothe switching fabric but which are standing by. Those multiplexers alsosend probe cells into the switching fabric, but due to lack ofconnections, they never receive any return cells. Consequently, themultiplexer makes a decision that it is in reserve. Not until the systemhas given the multiplexer an activation order, will the multiplexerstart to determine the connection port in the manner described above.

FIG. 9 shows the tables in the multiplexers after the connection portshave been determined. The question marks in the rows of FIG. 6 have nowbeen replaced with the indexes of the ports which have been determinedin accordance with the teaching of the present invention. A prerequisitefor the invention is that it is always known to which port the operationand maintenance unit 35 is connected. Here the port is 0.

The multiplexer 1 can now form a table, where the second row containsindexes of the bidirectional virtual connection to the operation andmaintenance unit. The indexes are Y+0, 0, and X. Subsequent rows areformed with a simple arithmetic algorithm as follows:

The third row contains indexes of the bidirectional virtual connectionbetween multiplexer 32, which is connected to port 1 and to theoperation and maintenance unit. The indexes are Y+1, 1, and X. Thefourth row contains indexes of the bidirectional virtual connectionbetween multiplexer 33, which is connected to port 2 and to theoperation and maintenance unit. The row is Y+2, 2, and X. If there aremore multiplexers as shown in FIG. 9, additional rows are formed in thesame way. For example, the row for a multiplexer connected to port K wasY+K, K, and X.

Multiplexer 32 forms a table containing only one row, which is X, 0,Y+1. These indexes connect through the bidirectional virtual connectionthe multiplexer to port 0, and from there to termination point Y+1,which refers to the third row of the table in multiplexer 31.Accordingly, multiplexer 33 forms a table containing only one row withthe indexes X, 0, Y+2. The indexes connect the multiplexer to port 0,and from there to the termination point Y+2, which refers to the thirdrow of the table in multiplexer 31.

As a result, the virtual connection between each multiplexer and theoperation and maintenance unit has been established. The multiplexerscan now communicate with the operation and maintenance unit and receiveconfiguration information. In addition, the multiplexers can communicatewith each other, wherein communication takes place through the operationand maintenance unit. For that purpose, the operation and maintenanceunit contains an application program which is intended for transferringmessages.

The present invention is applicable to any exchanges, with theprerequisites that information is transferred in fixed length packets orcells and that the number of the ports of the switching fabric is known.Moreover, the communication channels (i.e. row indexes) for theprocessors of the multiplexers must be determined in accordance with aknown algorithm.

1. A method of establishing virtual connections for transmission ofpackets of internal traffic in a broadband telecommunication switchcomprising a switching fabric having a plurality of indexed ports, theswitching fabric switching an internal traffic packet applied to aninput port to the output port indicated in the packet, a plurality ofprocessor units, an operation and maintenance unit which includes anapplication for communication with the processor units, a plurality ofmultiplexers, each connected to its own input port of the switchingfabric and multiplexing internal traffic packets into said input port,the internal traffic packets arriving from a group of processor unitsconnected to the multiplexer, said method further comprising the stepsof: generating, in each multiplexer, probe packets addressed to everyindexed port of the switching fabric, each probe packet containing anindex of an associated port; sending the probe packets to the switchingfabric; receiving probe packets from the switching fabric; concludingthat the multiplexer has been connected to that indexed port of theswitching fabric whose index is indicated in the received probe packets;and establishing virtual connections between each of the multiplexersand the operation and maintenance unit by binding connection identifierswith indexes of the ports indicated in the received probe packets. 2.The method as claimed in claim 1, wherein the index of the port islocated to the address field of the probe packet.
 3. The method as inclaim 1, wherein the multiplexer to which the operation and maintenanceunit is connected initializes a bi-directional connection for each ofthe multiplexers.
 4. The method as in claim 2, wherein said multiplexerforms a switching table comprising a row of indexes, the first indexreferring to a termination point within the multiplexer, the secondindex referring to a termination point within another multiplexer, andthe third index referring to the index of the port to which said othermultiplexer is connected, wherein each row identifies the virtualconnection between said multiplexer and another multiplexer.
 5. Themethod as in claim 3, wherein each of the other multiplexers initializesthe bi-directional connection for the multiplexer to which the operationand maintenance unit is connected.
 6. The method as in claim 5, whereinsaid other multiplexers form a switching table comprising one row ofindexes, the first index referring to a termination point within themultiplexer, the second index referring to a termination point withinthe operation and maintenance unit, and the third index referring to theindex of the port to which the operation and maintenance unit isconnected, wherein the row identifies the virtual connection between themultiplexer and the operation and maintenance unit.
 7. The method as inclaim 1, wherein in absence of received probe packets it is concludedthat the multiplexer is in reserve.
 8. The method as in claim 1, whereineach multiplexer forms an extra row including an extra termination pointand the index of the extra termination point is included in the probecell.
 9. The method as in claim 8, wherein the index of the extratermination point is included in the address field of the probe cell.10. The method as in claim 8, wherein the internal processor unit of themultiplexer is functionally connected to the extra termination point,whereupon the received cells are transferred to the extra terminationpoint and further to the internal processor unit.
 11. The method as inclaim 8, wherein the index of the extra termination point is the same ineach of the multiplexers.
 12. The method as in claim 1, wherein theoperation and maintenance unit sends configuration instructions to themultiplexers via the established virtual connections.
 13. The method asin claim 4, wherein the indexes in the rows identifying the virtualconnections are determined in accordance with a known mathematicalalgorithm.
 14. The method as in claim 13, wherein the first indexreferring to a termination point is a sum of a constant value and theindex of the port and the second index is the same as the index of theport.
 15. An apparatus, comprising: a generating unit configured togenerate, in each multiplexer, probe packets addressed to every indexedport of a switching fabric, the probe packet containing an index of theport; a sending unit configured to send the probe packets to theswitching fabric; a receiving unit configured to receive probe packetsfrom the switching fabric; a concluding unit configured to conclude thatthe multiplexer has been connected to that indexed port of the switchingfabric whose index is indicated in the received cells; and anestablishing unit configured to establish virtual connections betweeneach of the multiplexers and an operation and maintenance unit of atelecommunication switch by binding connection identifiers with indexesof the ports, wherein the apparatus is configure to establish virtualconnections for transmission of packets of internal traffic in abroadband telecommunication switch, the telecommunication switchcomprising the switching fabric having a plurality of indexed ports, theswitching fabric switching an internal traffic packet applied to aninput port to an output port indicated in the packet, thetelecommunication switch further comprising a plurality of processorunits, the operation and maintenance unit which includes an applicationfor communication with the processor units and a plurality ofmultiplexers, each connected to its own input port of the switchingfabric and multiplexing internal traffic packets into said input port,the internal traffic packets arriving from a group of processor unitsconnected to the multiplexer.
 16. An apparatus, comprising: generatingmeans for generating, in each multiplexer, probe packets addressed toevery indexed port of a switching fabric, the probe packet containing anindex of the port; sending means for sending the probe packets to theswitching fabric; receiving means for receiving probe packets from theswitching fabric; a concluding means for concluding that the multiplexerhas been connected to that indexed port of the switching fabric whoseindex is indicated in the received cells; and an establishing means forestablishing virtual connections between each of the multiplexers and anoperation and maintenance unit of a telecommunication switch by bindingconnection identifiers with indexes of the ports, wherein the apparatusis configure to establish virtual connections for transmission ofpackets of internal traffic in a broadband telecommunication switch, thetelecommunication switch comprising the switching fabric having aplurality of indexed ports, the switching fabric switching an internaltraffic packet applied to an input port to an output port indicated inthe packet, the telecommunication switch further comprising a pluralityof processor units, the operation and maintenance unit which includes anapplication for communication with the processor units and a pluralityof multiplexers, each connected to its own input port of the switchingfabric and multiplexing internal traffic packets into said input port,the internal traffic packets arriving from a group of processor unitsconnected to the multiplexer.